290 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



formation of a further quantity of sugar. In this conversion a number 

 of by-products are formed, which behave differently to iodine and to the 

 sugar tests, and in their action on polarized light. The following table 

 shows these changes in outline : — 







Rotation. 



Reducing 

 Power. 



Behavior 

 with Iodine. 



Other Tests. 



1. 



Soluble starch, 



. 218° 



6 



Blue. 



Precipitated by tan- 

 nic acid and alcohol. 



2. 



Erythrodextrin, 







Red. 



Not precipitated by 

 tannic acid and al- 

 cohol. 



3. 



Achroodextrin, 



. 210 

 . 190 

 . 150 



12 

 12 



28 



Colorless. 



" 



4. 



Maltose, 



. 150 



til 



" 



" 



5. 



Grape-sugar, 



. 58 



100 



" 



" 



If a little saliva be added to warm, thick starch-paste, in one or two 

 minutes the thick mucilage will be converted into a thin, watery fluid, 

 which will not yield either a dextrin or sugar reaction ; it will still give 

 a blue with iodine. This is, therefore, the first stage in the diastatic 

 action of saliva on starch — the formation of soluble starch. If a longer 

 time is allowed to elapse before the testing is performed, sugar may then 

 be found in the fluid, even though it gives a distinct blue with iodine. 

 A few minutes later, testing will show the presence of a larger quantity 

 of sugar, and if iodine be added a blue color will be produced ; but on 

 diluting this and adding more iodine a violet color will appear, showing 

 the presence of erythrodextrin, together with soluble starch and sugar. 

 After a short time iodine ceases to give a blue, but yields a deep-red 

 color, which later still yields to a yellowish-brown color, and finalhy no 

 color at all on the addition of iodine, while all the time the quantity of 

 sugar goes on steadily increasing. These reactions show that the soluble 

 starch gives place to erythrodextrin, giving a red with iodine, and finally 

 to achroodextrin, which has no color reaction with iodine; while, from 

 the fact that the sugar continually increases as these substances dis- 

 appear, it is evident that the sugar results from the progressive conver- 

 sion of these different forms of erythro- and achroodextrin into dextrose, 

 or some other form of sugar. Musculus and O'Sullivan have proved 

 that the sugar which results from the action of diastatic ferments on 

 starch is maltose, which is a fennentescible sugar belonging to the group 

 of saccharoses, having a formula of C^H^On. This substance rotates 

 the plane of polarized light 150° to the right, while dextrose has only a 

 rotatory power of +58°, while it has a reducing power for the cupric 

 oxide sugar test of 61°, as compared to grape-sugar, which may be placed 

 at 100°. 



In order to explain the above results it is necessary to assume that 

 the molecule of soluble starch is a composite molecule, composed of 



